Traditional oil and gas wells are drilled with boreholes extending from the surface vertically down to some depth to a pay zone. The pay zone contains the formation with the hydrocarbons of interest.
Some geological formations become more productive if the wells extend horizontally into and stay within the formations. Horizontal wells are initially drilled as vertical wells. At some depth, the borehole turns from vertical to horizontal. There is a radius of curvature of the borehole as it changes orientation from vertical to horizontal.
Many wells, after producing for some time, require artificial lift. For example, oil wells may require the oil to be pumped to the surface; gas wells may require liquid, such as salt water, to be pumped out so as to open the well to gas flow.
An example of one type of artificial lift mechanism is a sucker rod pump. A sucker rod pump has a barrel and a plunger located inside of the barrel. There is relative reciprocation between the plunger and the barrel, which reciprocation is provided by a string of sucker rods extending from the pump up the well to the surface.
In many horizontal wells, it is difficult to locate a sucker rod pump therein because the pump cannot traverse the curved portion of the well. The radius of curvature is too small for the length of the pump. In general, the deeper the well, the longer the pump that is needed. A long pump requires a relatively large radius in order to traverse the curve. In addition, pumps that can be installed in the horizontal section suffer from excessive wear from the sucker rod string pulling the plunger at an angle. There are also issues with the sucker rod guides wearing out allowing the sucker rod string to cut into the tubing.